It has been suggested that behavior patterns of aggression, impulsivity, and insensitivity to consequences describe, and perhaps contribute to, subsequent antisocial activity, including drug abuse. Little is known about how these maladaptive behavior patterns are related to each other; whether they collectively or independently contribute to antisocial activity; or how they are effected by marijuana. Recent data show an increasing trend in marijuana use, especially among teenagers, making it an important drug to investigate. The proposed experiments will examine, (a) whether individuals who tend to respond more/less aggressively on laboratory tasks also tend to be more/less impulsive and more/less sensitive to the consequences of their behavior; and (b) when marijuana produces a change in the aggressive responding of individuals, does it also produce similar, dose-related changes in impulsivity, and in sensitivity to consequences. The research design will use three laboratory-based operant tasks: the Point-Subtraction-Aggression Paradigm (PSAP C Don Cherek), a measure of aggressive responding; a two-choice discrete-trial task measuring impulsivity and self-control; and a concurrent random interval task (concurrent RI-RI) measuring sensitivity to changes in reinforcement density. All subjects will first be exposed to the PSAP following administration of placebo/marijuana (Phase I), then be exposed to either the impulsivity task (Phase 2, Experiment 1), or the concurrent RI-RI task (Phase 2, Experiment 2).